Lithium ion batteries and other lithium secondary batteries are miniaturized, have light weight, have high energy density and have excellent power density compared to existing batteries. Therefore, these batteries have been preferably used in recent years as so-called portable power sources for personal computers, mobile terminals and the like and vehicle driving power sources.
Such lithium secondary batteries are configured to comprise an electrode assembly having a positive electrode and a negative electrode and an electrolyte (typically electrolyte solution), which are contained in a battery case. Charging and discharge are carried out by means of transfer of lithium ions (Li+) back and forth between the positive electrode and the negative electrode. One of important members that determine the battery performances is a positive electrode material (positive electrode active material). Recently, olivine-type lithium-containing phosphate compounds (LiMPO4 (M: at least one element selected from Ni, Mn, Fe and Co); hereinafter sometimes merely referred to as “lithium-containing phosphate compounds”) having a crystal structure belonging to the space group Pnma have been attracting attention as positive electrode active materials allowing high energy density. Prior arts relating to the compounds may include Patent Literature 1 and Patent Literature 2.